1. Technical Field
This invention relates to a process for preparing organic acids by oxidizing in a liquid oxidation reactor an organic liquid with molecular oxygen or a gas containing molecular oxygen to produce an organic acid.
2. Background of the Invention
The manufacture of petrochemicals by the liquid phase oxidation of hydrocarbons with a gaseous oxidant is a very significant commercial operation. Examples of commodity chemicals produced by this process are terephthalic acid, adipic acid, and phenol. Air has traditionally been employed as the gaseous oxidant in such processes, however, it has long been recognized that significant process advantages are offered by using pure oxygen as the oxidant. Such advantages include, for example, improved mass transfer of oxygen into liquid phase because of increased concentration (partial pressure) driving force, improved chemical selectivity resulting from less severe operating conditions, reduced equipment size resulting from reduced gas throughput to the reactor, and reduced waste gas blowoff from the reactor.
However, safety is always a concern when using pure oxygen as the oxidant in any chemical process. There is a continuing need to provide safe and efficient processes for preparing organic acids especially when pure oxygen is used as the oxidant.
3. Disclosure of the Invention
This invention relates to a process for producing one or more organic acids in high purity which process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen, at a temperature sufficiently stable to prevent cycling of reaction rate, to produce a crude reaction product fluid, and (ii) refining said crude reaction product fluid to give said one or more organic acids in high purity. The oxidation temperature is preferably controlled to within about xc2x13xc2x0 C. of a target temperature. By so controlling the oxidation temperature, any temperature upsets will not cause the release of amounts of oxygen to the vapor space of the liquid oxidation reactor which may cause the vapor region to exceed the LOV as defined below.
This invention also relates to a process for producing one or more oxo acids in high purity which process comprises (i) oxidizing in a liquid oxidation reactor one or more oxo aldehydes with essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen, in which mass transfer between said one or more oxo aldehydes and said essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen is sufficient to minimize or eliminate byproduct formation, to produce a crude reaction product fluid, and (ii) refining said crude reaction product fluid to give said one or more oxo acids in high purity. By employing a liquid oxidation reactor as described herein, the forced circulation of the reactants, i.e., oxo aldehyde and pure oxygen or oxygen-enriched air containing at least about 50% oxygen, rapidly throughout the liquid oxidation reactor system enhances heat and mass transfer between the reactants, thereby maximizing volumetric reactor productivity and improving desired product selectivity.
This invention further relates to a process for producing one or more organic acids in high purity which process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen to produce a crude reaction product fluid, and (ii) refining said crude reaction product fluid to give said one or more organic acids in high purity; wherein said liquid oxidation reactor comprises:
a) a vertically positioned tube and shell reactor vessel having a hollow draft tube in the center thereof and heat exchanger tubes in the annular space between the hollow draft tube and the outer wall of the reactor vessel, said reactor vessel having an upper space above and a hollow mixing chamber below said hollow draft tube and said heat exchanger tube;
b) impeller means positioned within said hollow draft tube and adapted to cause the rapid flow of the organic liquid downward through the hollow draft tube into the bottom mixing chamber and rapidly upward through said heat exchanger tubes as a substantially uniform dispersion and into said upper space in the reactor vessel;
c) an upper chamber positioned above and in fluid communication with said reactor vessel, said upper chamber having a vapor space above a desired liquid level;
d) at least one generally horizontal gas containment baffle disposed between said upper chamber and said reaction vessel in such a manner that the vapor space above the liquid level in said upper chamber is maintained below both the LOV and LFL, said gas containment baffle being formed with a central hole to enable said impeller means to extend generally concentrically through said hole in said gas containment baffle;
e) at least one generally horizontal seal baffle disposed within the vapor space of said upper chamber in such a manner that the vapor space above said seal baffle is maintained under an inert atmosphere, said seal baffle being formed with a central hole to enable said impeller means to extend generally concentrically through said hole in said seal baffle;
f) conduit means for introducing said organic liquid into the reactor vessel and for introducing said pure oxygen or oxygen-enriched air containing at least about 50% oxygen into said reactor vessel or the upper chamber for rapid recirculation with the organic liquid downward through the hollow draft tubes into the bottom mixing chamber and rapidly upward through said heat exchanger tubes into said upper space;
g) conduit means for withdrawing product liquid from the reactor vessel;
h) conduit means for flowing cooling fluid to the reactor vessel for the removal of exothermic heat of reaction generated within said reactor vessel; and
i) control means for maintaining a desired liquid level within the reactor vessel or within the upper chamber. By installing a baffle in the upper chamber, any equipment or parts having the potential to generate frictional heat, e.g., a seal through which the agitator shaft passes into the liquid oxidation reactor, will not pose an ignition hazard if oxygen and organic vapors are prevented from contacting such equipment or parts in an upset condition such as loss of agitation in the reaction zone.
This invention yet further relates to a process for producing one or more organic acids in high purity which process comprises (i) oxidizing in a primary liquid oxidation reactor one or more organic liquids with essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen to produce a first crude reaction product fluid, (ii) removing said first crude reaction product fluid from said primary liquid oxidation reactor, (iii) feeding said first crude reaction product fluid to at least one secondary liquid oxidation reactor or plug flow reactor, (iv) oxidizing in said secondary liquid oxidation reactor or plug flow reactor said first crude reaction product fluid with essentially pure oxygen or oxygen-enriched air containing at least about 50% oxygen to produce a second crude reaction product fluid, and (v) refining said second crude reaction product fluid to give said one or more organic acids in high purity. By configuring two or more liquid oxidation reactors in series or a liquid oxidation reactor followed in series by a plug flow reactor, efficiency can be improved by increasing conversion of the organic liquid.